HP supercells and inflow

[ChristianT]

I feel like I should already know this and maybe I already do but I would like to ask how HP supercells work. I chased the April 26th cells in Stephenville, Texas and noticed all the tornadoes were wrapped in rain. I know that the best way to see these tornadoes would be to get into the inflow notch, though this is very dangerous to do. Does that mean that there is always some sort of opening that is rain free in the notch for inflow to keep coming in without being cooled by rain? I ask this because of the Elmer tornado this past weekend. At one point, it emerged from the rain only to be wrapped deeply inside of the core again and yet it went like over 30 miles, a lot of it while it was completely wrapped. Can the tornado continue to intensify and go even if the whole notch is closed?

 

[NealRasmussen]

I think rain wrapped, might be better thought of as 'rain spiraled'? As the inflow air might be going way up north of the circulation and wrapping back in on the west side. As the Yang of the RFD is wrapping way south of the circulation and wrapping back in on the east side. So unless the highway curves cyclonically just right...

HP's seem to me to be "wet RFDs". I hope a .edu person chimes in, but it seems to me the trajectory for the FFD and the RFD get mingled. When so much precipitable water, or weakish venting, the FFD isn't cast downstream enough and part of it, or in some cases most all of it, gets caught in the RFD flow and so comes out HP.

There's also the 'blob' that falls in situ to the center of the WC circulation. This rain/hail blob I've seen more and more sense it's discovery back, ummm, 10 years ago? During the Foss Lake tornado of Oct 9, 2001 the tornado emerged from a 'blob' of core. I could see the funnel quite well in the LCD, but not visually.
http://shaggybuffalo.com/days/20011009.htm (Not sure if those are even there anymore.)

My point is often I hear chasers lamenting the 'blob' as they think it's going HP. Well, maybe yes, and maybe no. Don't dismiss rain cores falling from wallcloud centers as always lowering chances of a tornado.

 

[ChristianT]

So basically the rain doesn't get carried by the FFD as much as normal and so it gets caught by the RFD and wraps around the mesocyclone. That's kinda what I thought I am just not good at using to many technical terms. I am a little confused as what this "blob" is. This sounds like the same thing as the wet RFD. Is it something different?

 

[Marshall Stoner]

I think cells classified as classic rather than high precip also have rain wrapping around the mesocyclone when they are about to produce a tornado. The precip is what produces the classic hook. It's typically thin enough to be almost transparent with a classic supercell (but still shows up on radar). The precip is also confined to the very northern edge of the RFD. The developing tornado circulation wraps/stretches the RFD precipitation into a thin sheath/filament while the apex of the RFD "bow" is dry.

With an HP supercell the entire RFD can be filled with precip, completely obscuring the tornado from any southern or western vantage point. In contrast to the classic supercell, the "hook" is thick while the dry inflow notch is a thin filament. You can sometimes trace the dry inflow notch to the tornado on high resolution radar, but in practice there's no way to see the tornado funnel without driving into it.

In practice the distinction between classic and HP structure is fuzzy. Sometimes a tornado forms while the parent storm is in the classic stage, but the RFD subsequently fills with rain and obscures the tornado. This is what happened with the 2013 El Reno tornado. The tornado was at its most intense stage during the transition from classic to HP. The thickening of the rain curtain actually helped the tornado grow in size. It grew and strengthened while it was becoming wrapped with rain.

 

[Marshall Stoner]

Someone correct me if I'm wrong, but in my understanding "the blob" is something seen on elevated radar scans. It descends near the northern edge of the RFD but it doesn't necessarily appear to an observer on the ground.

My own theory is that "the blob" forms when there's inertial instability occurring on the outer edge of the mesocyclone aloft. A lobe of precipitation is flung out of the updraft aloft. It then gets sheared into a thin filament as it descends. A tornado is likely to occur when the mesocyclone re-ingests some of this air after it's descended to the ground. Prior to a tornado you often see a thin sheaths of precipitation seeming to move in opposite directions. You'll see some moving from left to right and through that some moving from right to left. It's a thin amount of precipitation wrapping around the mesocyclone. It's thin enough that it might be hard to even see. You may have to look closely and squint your eyes.